Duplex telegraph system



June' l0, 1930. J. H. BELL DUPLEX TELEGRAPH SYSTEM Filed Feb. 28. 1928 /NVENTUR n .N mm @lm j pv/J N Patented June 10, 1930 d UNITED i STATES 'I PATENT OFFICE JOHN H. BELL, oEfsoUTH OEANGEANEW JERSEY, AssIeNoE To WESTERN ELECTEIC COMPANY,`INC., OF NEW YORK, N. YJ, A CORPORATION F NLffYOR'Kk y DUPLEX Y TEEEGEAVPH- `sYsriEivr l Application iled February 28,1928. Serial Noli-257,574. i

This inventionrelate's to duplex telegraph systems and 'more particularly to s ysteinsof this type in which grounded telegraphcircults are operated 1n conjunction with cable lines. A

The telegraph traiiic betweenlarge'and disitant vcities is ordinarily directed over a large number of conductors p'lacedyin close promity d to each other in a cable. i In order to'avoid disturbancesv from external sourc e's as"\ vellas the mutual disturbances between the circuits within the cable, such cable circuits are conimonly arranged ,with` a metallic return. Where the distances Vare vgreat repeater sta- 'tions are placed at suitable intervals in a well known 'Inanner'x- In order to utilize such a cable and its associated equipment to the best'advantage itis Y desirable that it should 'serve points located withincertain distanceson either side of the path of the cable. Telegraph stations located at a'dstance fromV the cable, hereinafter termed branch stations, would `ordinarily y be operatedl as, ;round edl` circuits over single open=wire lines. Whenv such circuits have been routed through a rsection ot ak cable,sit has hitherto been the practice to run the openwire line to the nearest repeater station and to insert a repeater therefor atthis point, -so

l '30 that Vthe open-wire section could'b'e operated on a grounded basis and the cable section on a metallic basis. This'hasbeen found'necessaryV since incase `an open wire 'circuitwfere connected directly without a repeater to a single conductor in a multifconductor cable,

in accordance Ywithk methods hithertoA employed, the transmitting effectiveness" of the circuit would bereduced as a result of eX,-

traneous interference. A ,.f

4c The4 present invention provides for a cuit arrangement whereby an open-wlreline from a distant branch 4station may-be connected to a cablek pair Awithout intervening equipment, and may .be cut in at the point 4,5V where it reaches the cable; without the necessity of running the line as an'. openfwire line along with the'` cable to a cable station. The

turbances'set up inthe pair by other similarly "manner that 'disturbances' entering cable pair is so connected,`and the repeaterY or terminal circmt so arranged, that d1sconnectedcable pairs are completely neu# tralized anddo notinterferewith thereception ofsignals at thecable station. Since in v'accordance with the present practice the distance betweenA cable stationsfis considerable,javeragingfabout 100 miles, substantial savings in line material and labor mayfresult from the adoption of aniarrangement''suchl as here proposed. Y: .y

' `In accordance with the present invention the cablestatiOn, whichmaybe either a rel vpeaterstation or a terminal station communieating with a *branchl station," includes a line relay with a Vplurality, of windings arranged symmetrically with respect to the local transmitting circuit.' One. conductor of the cable pair is' directly connected?atitsfar endto the open-wireline', and serves to tran'smit'the signals; the other, or return conductorpfis grounded at 'its far end -eitherfdirectly Vor through an, impedance and' serves' asa neu- 'tralizingconductor.` 'VThecable pair with its associated `open-wirey line and impedance is balanced with'respect Vto the transmitting circuit byvan artificial lifne'Y at the cable station, so that signalsmay bev transmitted without affecting the receiving relay at that station.

The-windings of the. line relay are, furthern more, connected to 4the cable pair in' sucha these windings,.arene-utralized therein.

` embodiment of the invention is sche` "matic'ally illustrated in the accompanying drawing inwhich vF 1 vshows: a general "Yarrangement of' a cable with its 'associatedjrel peater and' terminal stations and outlying' branch stations, andF 2 is a more detailed showing a branch stat1on,1a1cable station and' the interconnection therebetween.v

Referring particularly toFig. 1a cable'Y 10,

containing-a pluralitybf twisted pairs, of n which only a few such' ias 113, 14, 15`and; 16V Y have been. shown, ,extendsv between l terminal stations A, and Blandis ydivided into sections, by intermediate repeaterstationsjlE andF.

.Branch 'stations C vandiD'whichv inayf'be, lo-Y p cated atsome considerable distance from ,the d. Vline of thecable: are connectedby means of lopen-'wire line'sfll andVV 12, respectively, to

-certainpairs within the cable." Thus line 11 of the presence in the cable over that distanceV of an idle pair of conductors.

The line circuit for station C may be terminated at repeater E or may continue over the pair 16 to terminal station A, as shown.

The open-wire line 12 is similarly connected at point H to Vthe pair 14 which terminates at station B.

The latter circuit is shown more in detail in Fig. 2. Branch station D which is of the grounded duplex type, comprises a doublewound polarized relay 2O the windings of which are connected in the well known differential manner for duplex operation, to line 12 and to artificial line 21, respectively, and have their mid-points connected through transmitting key 22 to sending batteries 23 and 24. Relay 20 by its armature controls a local circuit for the sounder 25. Y

The cable station B is shown as a terminal station of the differential `duplex type comprising a four-winding polarizing relay 30 havingan armature for the control of the receivingequipment R, which may be of any desirable type such as a sounder. Transmitting key 31 and its associated sending batteries 32and 33 are connected in duplex relation to the windings of relay 30. The station B may, however, be a repeater station in which case the receiving equipment R and the key 31, and batteries 32 and 33 would be replaced by the receiving and transmitting equipment of a repeater in a wellknown manner. Y

i Thewindings 34 and 35 of relay 30 are each connected to a conductor of the pair v14, which, as shown in Fig. 1, is included in the cable 10 and terminates at point H. At this `point the line conductor of the pair 14 which is connected to winding 34, is brought out'and connected directly to the open wire line 12 and the return conductor n of the pair 14, which is connected to winding 35, issimilarly brought out and is connected to ground. The

impedance40 may be included in this ground -connection `for purposes which Vwill be den scribed hereinafter.

An artificial line 38 is connected to windings 36 and 37 of relay 30.

` The operation'of this system may be described as follows: It will iirst be assumed that a message'is being transmitted from station D to station B. The circuit may then f beI traced from either of the sending. batteries 23 or 24 over key 22. It divides into one branch through one winding of receiving relay 20, artificial line 21 to ground, and another branch through the other winding of relay 20, open-wire line 12, the line conductor of the pair 14, windings 34 and 36 of relay 30, artiiicial line 38 and winding 37 to ground. Relay 20 remains unoperated in this circuit. The windings of relay 30 are so wound and apportioned that thjey cooperate to control the armature of relay30, which thus repeats the received impulse into the receiving circuit R.

Next assuming that a message is being transmitted from station B to station D an impulse produced by the operation of key 31 at stationY B would take the following paths, `from either of the batteries 32 or 33, over key 31, then over two branches, one branch leading over winding 36, artificial line 38 and winding 37 to ground; the other the open-wire line 12 and its terminal station. The circuit arrangement shown in Fig. 2 thus provides for satisfactory duplex operation. Y

Since the impulses are transmitted over only one of the conductors of the pair 14 disturbances, due to such impulses, occur in the cable which, however, will not iniiuence the telephone or telegraph circuits which. utilize both conductors of their pairs. The conductors of such pairs are interposed by twisting and may be connected to the equipment at the cable stations in such a manner that the disturbances willibe neutralized. Y 'The invention is particularly directed to the prevention of disturbances in circuits such as shown in Fig. 2, where only one conductor of a cable pair is used for the transmission of signals. Let it be assumed that another `pair 17 serves to interconnect an open-wireline, such as 12, and a cable station, such as B. An impulse transmitted over the line conductor oit pair 17 would, on account of its close proximity thereto, induce a disturbing impulse in each of the conductors of pair V14. These disturbing impulseswould move in the same direction in the two Vconductors within the cable and consequently would produce opposite eiects in the windings 34 and 35. The impulse in ther l line conductor traverses windings 34, 36 and roo rio

ersing the other windings. kIn order that the opposite eiects of the impulses-upon relay may be equal and therefore be neutralized it is essential that the amplitudes of the 1nlduced impulses and their phase relation be properly governed by the impedances of the two paths. This may be attained by intro-V ducing an impedance 40`in the ground connection at point H, which should be substan- .v

tially equal to the impedance of the openwire line 12 with associated terminal equip;- ment. However, when the cable pair 14 is very long the effect of the impedance 4:0 may be negligible in which case this impedance may be eliminated and point H directly grounded.

What is claimed is.:

l. In a telegraph system, a wire line,- a duplex station for said line, Va

pair of conductors, additional conductors of other signaling circuits immediately adjacent to said pair, aduplex cable. station for said pair, said open-wire line being directly connected to the free end of one conductor of said pair, and means associated with the free end of the other conductor of said pair to balance said open-wire line with respect to ,Y said cable station.

2. In a telegraph system, two cable stations, a receiving relay at one of said stations, a cable for interconnection of said stations, an lopen-wire line, a groundedterminal Y station 'or said line, a point lof junction on said cable for said line located between said cable stations, a pair of conductors in said cable connected to said relay, a connection to ground and a connection to said line for said pair of'conductors at said point of junction.V 3. In a telegraph system, an open-wireline, a grounded terminal station for said line,'a multi-conductor cable, a cable station for said cable, a receiving relay at said cable station, a first conductor in saidcable for direct interconnection of said line and said receiving relay, a second` conductor in Vsaid cable arranged to form a twisted pair with Y said first conductor, and connected to said re-k Y v ceivlng relay, and a ground connection at the free end of said second conductor.

In witness whereof, I hereunto subscribe my name this 24th day of February, 1928.

- JGHN H. BELL.k

singlev open# 

